Orchards are generally surveyed and maintained in rows, but various factors may introduce slight offsets within a row. For example, if one side of a row has more sunlight than the other, the tree may grow towards the sun. Additionally, human operators are used to hedge the trees and may hedge one side of a row more than the other introducing an offset. The offset results in a new centerline for the row. The end result is that even a well surveyed orchard has variation in row centers.
In a traditional orchard vehicle operation, a human operator in the cab reacts to visual and auditory cues to sense a middle area between trees in a row and steers the vehicle towards that middle area. The goal is to avoid contact with the trees which may damage the vehicle or trees.
An unmanned autonomous vehicle within an orchard row can be guided by GPS and a map. If the map is out of date compared to the centerlines of the row, which may have been redefined after the last hedging, the vehicle may drive with an offset relative to the center. The offset may cause the vehicle to heavily contact the trees and damage either the trees and/or the vehicle.
Cameras, radars, lasers, and ultrasonic sensors have been used in guidance systems to detect the distance to the crop or trees and in order to attempt to center the vehicle based on the distance measurements. Such systems are expensive and prone to damage due to optics, radomes, or openings. Additionally, they have difficulty detecting heavy contact with the tree if the tree is close to the sensor itself.